This invention relates to a method of separating chlorine from a mixture with other gases. In particular, it relates to contacting such a mixture with dichlorotoluene, which absorbs the chlorine.
Chlorine is shipped as a pressurized liquid in tank cars. Customers use the chlorine by typically forcing it out of the tank cars with air or nitrogen pressure. When the tank cars are returned to the chlorine manufacturer, they are filled with gases which contain some of the chlorine that was not removed. Gas mixtures that contain small amounts of chlorine and relatively harmless other gases also come from barges, plant vents, and other sources, and are known as "vent gases" or "blow gases." Because these gases contain chlorine they cannot be vented to the atmosphere.
Vent gases can be passed through an absorber column where the gas contacts liquid carbon tetrachloride. The carbon tetrachloride absorbs the chlorine and the chlorine-free air can then be vented to the atmosphere. The carbon tetrachloride containing the absorbed chlorine is heated to vaporize the chlorine. The vaporized chlorine is liquefied and recovered and the carbon tetrachloride, now free of chlorine, is recycled to the absorber column.
The problem with this chlorine recovery process is that small amounts of carbon tetrachloride vaporize and are vented to the atmosphere with the air. Because regulatory agencies have determined that carbon tetrachloride is an ozone depleter, the use of carbon tetrachloride as a chlorine absorber is no longer permitted and other solvents are now being used for this purpose. See, for example, U.S. Pat. Nos. 5,308,383 and 5,437,711, herein incorporated by reference.